One poster says: "Terrorists need communications. They often collect and use many anonymous pay-as-you-go phones, as well as swapping sim cards and handsets.

"If you're suspicious of the number of phones someone has, we need to know."

Obviously I'm in favour of finding and capturing terrorists on public transport or anywhere. But I really think that the ownership of mobile phones as an indicator of terrorism could be turning on the "fear factor" too much. A huge number of people I know have two mobile phones. Jag from Route79 also noted this.

Up until recently I had two mobile phones - one for work and one for personal use.

Admittedly, we were all from a "mobile heavy" demographic, but the point remains that most people have good reasons for using "several" mobile phones. Perhaps the police ads should have focussed more on the other "suspicious" behaviour such as people buying large quantities of chemicals.